Thienyl sulfonamide compounds are known as endothelin receptor antagonists. For example, sitaxentan, also known as N-(4-chloro-3-methyl-1,2-oxazol-5-yl)-2-[2-(6-methyl-2H-1,3-benzodioxol-5-yl)acetyl]thiophene-3-sulfonamide, is a compound that has been marketed for the effectiveness for pulmonary arterial hypertension and other conditions (Patent Literature 1).

However, the structure of sitaxentan includes a benzodioxol ring, and in general, compounds having such benzodioxol rings are converted to chemically highly reactive metabolites when metabolized by cytochrome P450 (CYP), and are known to irreversibly inhibit the activity of CYP by inactivation based on the covalent binding with CYP (Non Patent Literatures 1-3). Sitaxentan itself is known to have CYP inhibitory activity, and there have been several reports of drug-drug interactions with clinically used medications. To solve this problem, a compound has been developed having a deuterium atom substituted for a hydrogen atom on the methylene carbon of the benzodioxolyl group of sitaxentan, but no such compound is yet in commercial use, and the effects have been unsatisfactory (Patent Literature 2). Also, it is known that compounds containing deuterium generally require higher production costs. As a consequence, to solve this problem there is a need for a method that does not use deuterium.